There is no clear-cut "best" round for coyotes under 100 yards. There's a slew of cartridges that will do the job just fine. Anything more than a .22lr will more than likely cleanly take a coyote at that range with a well placed shot. The "ideal" round IMO would be any center fire cartridge .257 or smaller with a rapid expanding "varmint" bullet lighter than 85 gr or so. But taking coyotes at under 100 yards is not a very hard task, lets not over think this one